[Conclusion] dynamic Lambda expression Construction

 

Go directlyCode:

 VaR Ints = New   Int [] { 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9  }; //  VaR r = ints. Where (I => I> 5 );  //  Expression to be implemented  //  Create parameter I              VaR Parameter = Expression. parameter (  Typeof ( Int ), "  I  "  );  // Create constant 5              VaR Constant = Expression. Constant (  5  );  //  Create a comparison expression I> 5              VaR Bin = Expression. Equal (parameter, constant); Bin = Expression. Or (bin, expression. Equal (parameter, expression. Constant ( 3  )));  //  Obtain lambda expressions             VaR Lambda = Expression. Lambda <Func < Int , Bool > (Bin, parameter );  //  Get the delegate using the compile Method              VaR _ R = Ints. Where (lambda. Compile ());  Foreach ( VaR V In  _ R) response. Write (V + "  <Br>  " );

 

 

Build a dynamic Lambda expression for a custom object:

 

 Public   Class  Student {  Public   Int Id { Get ; Set  ;}  Public   String Name {Get ; Set  ;}}  //  Build Test Data  List <Student> students = New List <student> (); Students. Add (  New Student () {id = 1 , Name = "  Zhang San  "  }); Students. Add (  New Student () {id = 2 , Name = "  Li Si  "  }); Students. Add (  New Student () {id = 3 , Name = "  Wang 'er  "  }); Students. Add (  New Student () {id = 4 , Name = "  Li Xiaolan "  }); Students. Add (  New Student () {id = 5 , Name = "  Huang Wu  "  });  //  Construct a parameter expression  VaR Parameter = expression. parameter ( Typeof (Student ), "  Student  " );  //  Construct an object attribute expression  Memberexpression = Expression. Property (parameter, "  ID  "  );  //  Build constant expressions  VaR Constant = expression. Constant ( 1  );  //  Expression combination effect equals to student => Student. ID = 1 VaR Bin = Expression. Equal (memberexpression, constant );  //  The expression combination effect is equal to student => Student. ID = 1 & Student. ID = 2  Bin = Expression. Or (bin, expression. Equal (memberexpression, expression. Constant ( 2  )));  //  Obtain lambda expressions              VaR Lambda = Expression. Lambda <Func <student, Bool >(Bin, parameter );  VaR _ R = students. Where <student> (Lambda. Compile ());  Foreach (Student s In  _ R) {response. Write (S. Name + "  <Br>  "  );} 

 

Display result:

Zhang San
Li Si